Signaling system



April 5, 1938. s, NELSON 2,113,217

SIGNALING SYSTEM Filed June 22, 1937 8 (mm. COEFE RES/STANCE INVEN TOR.-S. F NELSON w W ATTORNE Patented Apr. 5, 1938 UNITED STATES PATENTOFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation oi New York Application June 22,

4 Claims.

This invention relates to signaling systems, and its objects are toincrease the responsiveness of signal operating devices, to enablepositive signal indications to be obtained under varying condi- 5 tionsof signaling current, and in general to improve the usefulness of suchsystems.

It has been the common practice in the past to signal over communicationcircuits, such as telephone trunks and toll lines, by sendingalternating signaling current over the circuit to operate a responsiverelay at the distant end.

The signal responsive relay in operating usually eflects the operationof other relays which close the circuits for the operation of visual oraudible signal devices. Since the signaling current is applied to theline for a limited time, it is necessary to provide some means forlocking the responsive relays to insure the continuance of the signalindications after the signaling current has ceased to flow.

In accordance with the present invention improvements are secured overthese prior art signaling arrangements by providing a signal responsiverelay which responds to the alternating current signals incoming overthe line and utilizes these currents to effect the energizatlon of oneof its windings from a local source to lock the relay in operatedcondition after the incoming signaling currents have ceased to how, More0 specifically the signal responsive relay is provided with twowindings, one of which is connected to the line for receiving thealternating signaling current incoming from a distant point,

the other winding being normally closed in a local circuit including asource of current and a resistor having a normal resistance which is toohigh to permit the flow of sufllcient current in the local circuit toenergize and operate the signal relay. The two windings of the relay,however, are arranged in inductive relation, and the alternatingsignaling currents flowing in one winding induce currents in the otherwinding which flow through the resistor to raise its temperature. Theresistor, having a large negative temperature coefllcient, immediatelylowers its resistance in response to these temporary induced currents,andln so doing allows an increased current to flow from the localsource. This increased flow of current from the local source maintainsthe resistor at a low value and also supplies sufllcient energy to therelay to hold it operated when the alternating signaling currents havesubsided. The relay in operating operates a signal lamp or otherindicating device to attract the attention of an operator.

1937, Serial No. 149,599

The drawing accompanying the detailed specification herein discloses acommunication line extending from one operator's position to another andequipped with a signaling circuit arrangement in accordance with thepresent invention.

Referring particularly to the drawing, an operator's position at theexchange A is provided with a connecting cord circuit C equipped withthe usual relays, lamps, and other devices, not shown herein, and alsoprovided with a source of ringing or signaling current I-. Acommunication circuit or line 2 appears in a connecting jack I! at theoperator's position in office A and extends to a distant exchange Bwhere it appears in a terminal jack it at an operator's position,represented by a cord C-l. The incoming end of the line 2 in exchange Bis equipped with a signal-responsive relay 3 having .two windin I and 5.The winding 4 is connected across the tip and ring conductors of theline i and in series with a condenser 6. The winding 5 is connected in alocal circuit including a direct current battery I, a resistor 8 havinga negative temperature coefllcient of resistance and a normallyc'losedcontact of control relay 9. Although the winding 5 is in anormally-closed circuit, the resistance of the element 8 is so high thatno appreciable current flows through said winding. The resistor I may bemade of any suitable material, such as boron or silver sulphide, whichare known to have high negative temperature coefllcients of resistance.The armature on the relay 3 controls a circuit for the calling lamp in,which is individual to the jack II at the operator's position.

A description will now be given of the manner in which the systemoperates. Assume that the operator at exchange A desires to call theoperator at exchange B over line 2 for the purpose of establishing acommunication connection. The operator at exchange A inserts the plug llof her cord C in the jack l! of line 2 and manipulates her ringing keyit to connect the ringing source I to the line. Alternating current fromthe source I flows over the line 2 through the condenser 6 and thewinding I of the relay 3 at the distant exchange. Relay 3 may or may notoperate, depending on the duration and on the intensity of the appliedringing current. However, the signaling current flowing through thewinding l induces a potential across the winding 5 by reason of the factthat the windings 4 and 5 are wound in close inductive relation to eachother on the common core. The potential across the winding 5 is appliedto the resistor 8 and causes enough current to flow through the resistorto increase its temperature and consequently lower its resistance. Thelowered resistance or the element 8 permits current to flow from thebattery 1 through said resistance and through the winding and inwillcient volume to operate and hold the relay I in operated condition.The operated relay 3- closes a circuit to light the lamp HI. Moreover,the flow of current from the battery 1 maintains the resistor 8 at itslow resistance because of the well-known characteristics of thesenegative resistance materials. When, therefore, the signaling current iswithdrawn from the line 2 by the release 01' the operator's key ii, thesignal relay 3 remains operated because of the energization of itsholding winding 5. The operator at C-l, observing the lamp l0, repliesby inserting the plug of her cord circuit in the jack ll 01' theincoming line. This operates relay 9, which opens the circuit oi thewinding 5 and the resistor 8, permitting the relay 3 to release andpermitting the resistor 8 to cool immediately and raise its resistanceto its normal, high value. The lamp I0 is extinguished, and theoperators may now converse with each other.

It will be obvious to those skilled in the art that the relay 3 may varyas to the details 01 its construction and the manner in which thewindings are assembled on the relay structure. The resistance values ofthese windings and the inductive relation between them may of course bedesigned to best meet the requirements for any particular use. Forexample, the relay 3 could be replaced by a transformer, having thebattery l, resistor I, and a relay for closing the lamp circuitconnected in series with the secondary winding. Moreover, it will beobvious that the present invention is applicable to a wide variety ofsignaling circuits and systems.

What is claimed is:

1. In combination, a relay having an operating winding and a holdingwinding, a circuit for said holding winding including a source ofcurrent, circuit means for delivering signal current to said operatingwinding to induce a potential across said holding winding, and aresistor having a normal high resistance included in circuit with saidholding winding and responsive to the induced potential to lower itsresistance and permit' the flow of current from said source to hold therelay operated.

2. The combination in a signaling system of a relay having an operatingwinding and a holding winding, a circuit for said holding windingincluding a source 01 direct current, circuit means for deliveringalternating signaling current to said operating winding to induce apotential across said holding winding, a variable-resistance elementhaving a normally-high resistance for preventing the energization ofsaid holding winding by said direct current source and responsive tocurrent induced in said holding winding to lower its'resistance andpermit the flow of current from said source sumcient to hold the relayoperated. and means controlled by said relay.

3. The combination in a signaling system of a source of direct current,a variable-resistance element having a normal resistance suflicientlyhigh to prevent the flow of current therethrough from said source, arelay having a winding thereon, a circuit for said winding includingsaid direct current source and said variable resistor, an operatingwinding on said relay arranged in inductive relation with saidfirst-mentioned winding, and circuit means for supplying alternatingcurrent to said operating winding to induce in said first-mentionedwinding and in the circuit thereof a current for heating said resistanceelement and causing its resistance to decrease to permit an increasedflow of current from said direct current source through saidfirst-mentioned winding.

4. The combination in a signaling system 01 a relay having a winding anda normally-closed circuit for said winding, a source 01' currentincluded in said circuit, a variable-resistance element in said circuitand having a normal resistance sufliciently high to preventthe flow 01'energizing current in said circuit and through said winding, anoperating winding for said relay wound in inductive relation with saidfirst-mentioned winding, means for supplying said operating windingtemporarily with operating current to induce current in said secondarywinding and in the circuit thereof, the induced current flowing in saidsecondary winding serving to lower the resistance oi said element,permitting current to flow from said source to hold the relay inoperated condition and to maintain said resistor at a low-resistancevalue after current ceases to flow in said operating winding, andsignaling means controlled by said relay.

' STANLEY F. NELSON.

